1. Field of the Invention
The present invention relates to the field of stretcher bar frames (stretcher bars) and canvas fastening. More particularly, this invention is a unique and improved stretcher bar system using slide fitting, interchangeable, variable length side bar segments, fixed ninety degree corner segments, internal connecting segments, and adjustable cross brace segments, allowing for lengthening or shortening of the sides of the stretcher bars and cross brace extensions. It features internal connecting segments with an interlocking pins mechanism, and connecting cross brace segments with an interlocking nut and bolt mechanism, for easy assembling/disassembling of the stretcher bars and cross brace segments. The stretcher bars and canvas fastening system also provides for easy mounting, re-stretching, dismantling, transporting and remounting of fine art canvases to an array of configurable stretcher bar frame sizes.
2. The Prior Art
In the field of fine art, canvas paintings are traditionally mounted to a permanent, non-adjustable, wooden frame comprised of wooden sections referred to as stretcher bars that provide a taunt support for artist stretched canvases. The stretcher bar wooden sections are assembled by means of interlocking dove-tail edges wedged together to form non-exact, ninety degree corners. Wooden tightening wedges are used to adjust corners to produce a perfect square. Cross braces are sometimes used as a stabilizing tension brace. Canvas or other material is stretched around and over the front perimeter of the stretcher bars and affixed to the back side by conventional means using staples or nails.
In general, current commercially known wooden stretcher bars are made and sold in fixed size bars or pre-assembled frame sizes and cannot to be customized in length and width. Several other limitations of wooden stretcher bars include difficulty in forming exact ninety degree corners, affordability, and transporting of large depth stretcher bars. A limited number of adjustable frames that expand or contract in some manner are known. These adjustable frames have various limitations and are difficult to use. U.S. Pat. No. 4,519,151 discloses a hollow tubular metallic frame coupled together at the end by a co-acting pair of corner elements. The frame size can be selectively expanded and contracted by inserting one of five fixed lengths of tubular frame side elements. Major disadvantages of this design is its limited non-combinable fixed length dimensional sides and round tubular sides that are not generally used in the field of fine art or acceptable by galleries. U.S. Pat. No. 4,144,660 discloses an adjustable canvas stretching frame of separate, interchangeable, uniform frame segments, which can be interconnected to form a limited number of small rectangular or square frames. The primary feature of this device is to provide a means to maintain an overall rectangular shape of the frame, adjust gaps between adjacent segments of the frame, and to provide a taut surface by adjusting the tension within individual frame segments, so a canvas can be re-stretched without damaging the canvas and/or removing the canvas from the frame. Several shortcomings to this mechanically complex design include its numerous parts and special hardware required for its assembly. Additionally, it does not allow for a canvas to be easily removed and reused. U.S. Pat. No. 6,253,471 discloses an adjustable canvas stretching frame with fixed corners and non-connectable, fixed wooded sides, which require cutting to a desired length and width. Several labor intensive shortcomings to this design include advance knowledge of woodworking technique, tools to cut wood to exact length and width for the sides, a drill to cut circular apertures, a router for notches, and metal screws to secure the frame. When a different side length or width is desired, additional wood and woodworking skills are required. U.S. Pat. No. 6,895,701 discloses an adjustable metal strainer frame for mounting art canvas eliminating conventional welding and hardware item such as rivets, nuts, and bolts. Major shortcomings to this design include having to cut metal sides to fixed lengths when a different side length or width is desired, the inability to connect side members to form longer or shorter side lengths, and the need to use bracing and hardware to form a secure ninety degree corners. U.S. Pat. No. 6,675,510 discloses a lateral and longitudinal mechanized edge gripping method to avoid uneven stresses, distortion, corner wrinkles, and tearing of canvas. It primarily allows for removal and remounting of the canvas but the disadvantage is that its difficulty to evenly stretch canvas due to interference from and canvas grippers. Additional and various other prior art is also cited in U.S. Pat. Nos. 3,482,343, 4,144,660, 4,179,830, and 4,519,151, and is incorporated herein by reference.
The above framing and stretching canvas references are primarily for attaching or remounting of canvas and do not allow for modifications in the overall size of the stretcher bar frame. The prior art is not designed to easily adjust for any lengthening, shortening, or correcting a canvas due to changes in environmental conditions, nor do they provide the capability or means, without prior training, skill, experience, or strength, to quickly and easily assemble/disassemble, or lengthening/shortening the stretcher bar frame to other frame configurations. The prior art does not allow the cross brace to be adjusted to match modification in the stretcher bar frame. The prior art does not allow the stretcher bars to be easily dismantled for compact storage and for less costly transport. It also does not address the need for affordable large stretcher bars.